>>I tried to use Defox without success. It gives some error like "bad .FXP" or something else like that.

I recall that was an issue with an earlier version of Defox. The latest version seems to work without trouble. Also there is an issue re Registry changes for the protection scheme on OS with UAC but that's easily overcome by escalating privileges to register your PC.

Alternatively, Refox also provides good protection in 2016 though it does attract a fee.

>>I know good users (I'm not one of them) can open Enigma protected files easly but my users not these type users... :)

From memory you have a strong client base using your retail system. It's possible people already are trying to scoop your code to see if they can compete or undercut. At present there's protection by obscurity: there are full hack instructions on some of the Chinese bulletin boards that can be accessed via online translators, and it used to be possible to download a zip file with required code and instructions so anybody could do it.